1. Field of the Invention
The present invention relates to a device for measuring longitudinal acceleration of vehicles, and more particularly, to such a longitudinal acceleration measuring device that is immune to static and dynamic errors.
2. Description of the Prior Art
A device for measuring longitudinal acceleration of a vehicle is well known and widely used in the art of automobiles, particularly in the art of the modern vehicle stability control using the microcomputers. Examples of those vehicle stability controls are shown in U.S. Pat. No. 5,702,165, U.S. Pat. No. 5,704,695 and U.S. Pat. No. 5,839,798. Those vehicle stability controls employ microcomputers to make vehicle stability calculations during the driving of the vehicles based upon various input signals in which the longitudinal acceleration of the vehicle is included.
As a matter of principle, a sensor for measuring longitudinal acceleration of a vehicle is operable with a pendulum adapted to shift forward or rearward relative to a housing which suspends the pendulum to be so swingable in response to an inertial force applied thereto according to a deceleration or an acceleration of the vehicle. Although a longitudinal acceleration sensor is generally one of the most important parameter sensors in most of the vehicle stability controls, errors in the measuring operations of the longitudinal acceleration sensors were cared for in none of those prior art controls. Nevertheless, the sensors for measuring the longitudinal acceleration of vehicles are inherently bound with static and dynamic errors which should be called external errors, because they are not such errors that will occur in the measuring device itself but they occur in a phase of the pertinent physical phenomenon transmitting to the sensor as a longitudinal acceleration. The static error is due to a longitudinal inclination of the road surface on which the vehicle is driven, while the dynamic error is mostly due to a temporal longitudinal oscillation of the vehicle caused by a small convex or concave deformation of the road surface.